CAT C15 ACERT 475hp MXS - low boost

CAT C15 ACERT 475hp MXS built in 2005 put in service in 2006. Installed CAT Heavy Haul software in March 09 and was very happy with performance. Performance has gradually gone downhill and boost has flatlined at 32 lbs. On PARS: fuel flow rate good, and remained good through all testing, but boost only reached max of 32 lbs. on both sides of engine; pinched off wastegate & air compressor, reran-no change; pressure tested from turbo inlet to cylinder head inlet-no leaks; removed air cleaner, reran-no change; put on new high-side turbo, reran-no change; put on new low-side turbo, reran-no change; unhooked mufflers, reran-no change; put in new injectors, reran-no change;
Does anyone have any idea where the boost is going?

CAT C15 ACERT 475hp MXS built in 2005 put in service in 2006. Installed CAT Heavy Haul software in March 09 and was very happy with performance. Performance has gradually gone downhill and boost has flatlined at 32 lbs. On PARS: fuel flow rate good, and remained good through all testing, but boost only reached max of 32 lbs. on both sides of engine; pinched off wastegate & air compressor, reran-no change; pressure tested from turbo inlet to cylinder head inlet-no leaks; removed air cleaner, reran-no change; put on new high-side turbo, reran-no change; put on new low-side turbo, reran-no change; unhooked mufflers, reran-no change; put in new injectors, reran-no change;
Does anyone have any idea where the boost is going?

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Hi mile-high: what did the heavy haul program do for the truck when things were going the way they should? Thanks for your time... david

Do you mean it was PAR dynoed? have you checked fuel pressure? what sort of truck is it in? freightliner accel pedal assemblies wear out causing low power with no other symptoms. Have you had the valve clearances checked?
Check if intake air temp is ok, faulty control valve for the JWAC will cause high intake air temp and low power.

Jas is onto one of the usual problems also by suggesting fuel pressure. so good advice there.

The fuel pumps have an unacceptable spring that will not maintain sufficient fuel pressure in these Acerts Even if you buy a New Fuel pump it will have the shorter spring in it. However there is a longer and heavier spring available that will hold up better than just stretching the old spring which is what many do now. You must have at min of 100PSI fuel pressure over 1200RPM. And usually in excess of 75PSI at Idle.
Cat says 75PSI at Full noise is within specs but that is Frog ##### and these things are so tight in the fuel tables for the Emissions that even low fuel pressure will cripple them.

This is the New longer spring replacement kit Part number 339-4983 from Caterpillar which fits the later pumps only like whats on most ACERTS. The one with the allen key plug on the relief valve.
The earlier ones with the 5/8 plug need to be shimmed like PaulE mentioned above.
Just remember even if you buy a Brand new Pump it will have the short spring it it... No idea why Cat do this crap but buy a spring and keep that Fuel Pressure up there.

This is the New longer spring replacement kit Part number 339-4983 from Caterpillar which fits the later pumps only like whats on most ACERTS. The one with the allen key plug on the relief valve.
The earlier ones with the 5/8 plug need to be shimmed like PaulE mentioned above.
Just remember even if you buy a Brand new Pump it will have the short spring it it... No idea why Cat do this crap but buy a spring and keep that Fuel Pressure up there.

Here is the Cat Service mag on it if anyone's interested

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A friend got this new spring kit for 6NZ only gained 8 psi.

Far call , reading your post sounds like your saying you cant shim on most Acerts. am i reading this right ? my MXS with allen head plug is shimmed.

You can shim both if you want. The old 5/8 plug was hollow and you could sit the shims in that.
The Allen head plug on the later ones is not hollow so you need to fit shims ontop and they need to have a hole in them to go over the spiggot.

The later spring is a bit longer and "should" hold a set for longer as its supposed to but it will drop also.

What I do is to drill and tap the plug and fit an adjusting screw with sealing Nut and then adjust it to the perfect pressure.

Make sure you have checked all other items in the fuel circuit first including.
The o ring on the bleed valve
The Filter both primary and secondary
The filter head Check valve
The filter head bypass valve
Sucking air
etc etc
Low fuel pressure not only causes low power but also causes cavitation in the injectors and they wear out much faster.